RU2796835C1 - Method for obtaining dressed carbon fibres and polyesterimide composites based on them - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: production of structural products using additive techniques. Proposed is a method for obtaining sized carbon fibre by applying a sizing, which is a mixture of polyesterimide 2.46-2.08 wt.% and di(4-aminophenyl)methane 0.04-0.42 wt.%, onto carbon fibre from a solution with a mass concentration 0.32% in chloroform followed by a stepwise rise in temperature to 60°C and simultaneous distillation of the solvent under the action of ultrasound with an operating power of 46 kHz, the finished carbon fibre obtained by the proposed method, and the polyesterimide composition, which contains 80 wt.% of the polymer matrix based on polyesterimide and 20 wt.% of the proposed finished carbon fibre.

EFFECT: improved melt flow and impact strength parameters of the created polyesterimide composition due to the introduction of a sizing composition, which increases the wettability of the filler and increases the boundary interactions between the filler and the polyesterimide matrix.

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Description

The invention relates to a method for producing finished carbon fibers and polyesterimide compositions with inorganic, in particular, carbon fibers as fillers, and can be used for the production of special-purpose structural products in additive technologies.

One of the ways to improve the performance characteristics of carbon fiber polyesterimide compositions is to finish the carbon fiber surface, which makes it possible to modify the structure of the interfacial layer and increase intermolecular adhesive interactions at the polymer-filler interface.

Couplings are substances that affect the structure, properties and length of the interfacial layer, which greatly increases the contact area of the fibrous filler with the binder. For the production of structural polymer composite materials with desired performance characteristics, it is necessary to purposefully select a sizing composition for a reinforcing fiber, taking into account the viscosity of the binder, its molecular weight, physicochemical properties, size and structure of pores in the filler. Thus, the development of sizing compositions for the production of polymer composite materials based on superstructural thermoplastics will improve the mechanical, heat-resistant, and operational properties of the material, which will lead to an increase in the service life of products.

From the prior art, various types of sizing additives are known that are used in the creation of a polymer composite material. So the patent for the invention RU 2057767 describes a polymer composite material, including a polysulfone matrix and carbon fibers, and the carbon fibers contain on the surface as a sizing layer a copolymer consisting of units of methacrylic acid, diethylene glycol and benzosulfonic acid in a molar ratio of 49.5:49 ,5:1 to 49: 49:2 in the amount of 0.52 - 5.0% by weight of the fiber in the following ratio, wt.%: carbon reinforcing fibers containing a copolymer, 25 - 75; polysulfone matrix rest. According to the authors of the invention, the use of said copolymer as a sizing layer makes it possible to increase the interlaminar shear strength of polysulfone carbon plastics by a factor of 1.8 - 2.2. The main disadvantage of the proposed solution is the use of an aqueous medium for applying a mixture of monomers to a carbon tape. Since carbon fibers and tapes are hydrophobic, it is difficult to achieve a uniform distribution of an aqueous solution of a mixture of monomers. As a result of polymerization, incomplete conversion of monomers is also possible, which can lead to the formation and release of water at other stages of obtaining a polymer composite, which will lead to the formation of pores and a decrease in strength characteristics. The presence of benzenesulfonic acid in an aqueous medium can also lead to the accumulation of ions, which can worsen the dielectric properties.

Known polymer compositions according to the patent of the Russian Federation No. 2201423, obtained on the basis of a polymer binder (sizing) and fiberglass or carbon filler. Preliminarily, a binder - oligomer is obtained by reacting aromatic tetracarboxylic acid tetranitrile and aromatic bis-o-cyanamine at a temperature of 170-180°C. The binder is obtained in powder form. The main disadvantage of the above solution is the complexity of the binder synthesis process. An incomplete degree of conversion of monomers during synthesis can lead to the release of low-molecular by-products of the reaction when combining the binder with the filler at an elevated temperature, and, consequently, to the formation of voids in the composite material, which will lead to a deterioration in the strength characteristics of the material. In addition, powdered finishes may not cover the surface of the filler evenly enough.

Polyetherimide composites are known according to US patent No. 4049613. To increase the wettability of carbon fiber by a polymer matrix, the patent proposes to keep the filler in hot nitric acid for three days, which is technologically and economically disadvantageous.

In the following work - according to the patent of the Russian Federation No. 2054015 "Method of sizing carbon fiber for the production of polysulfone carbon fiber", it is proposed to mix with a solvent a block copolymer consisting of units of bismethacryloyloxydiethylene glycol phthalate and bismethacryloyloxy-triethylene glycol phthalate, impregnation of the carbon filler, followed by drying to remove the solvent and polymerization of the sizing film on the fiber , characterized in that the mixing is carried out in water with simultaneous exposure to ultrasonic radiation at a frequency of 15 to 44 kHz and an exposure time of 5 to 14 minutes. The disadvantages of this method are the use of aqueous solutions of block copolymers for wetting hydrophobic surfaces of carbon fiber and the need for further polymerization on the surface of the filler. The result may be uneven wetting of the filler, and, consequently, the deterioration of the properties of the resulting carbon fiber.

The closest analogue is the method of finishing carbon fiber according to RF patent No. 2712612 "Method of obtaining finished carbon fibers and composite materials based on them." The disadvantage of the solution can be considered low values of the melt flow index and impact strength of polyesterimide compositions.

The objective of the present invention is to develop a method for producing sized carbon fibers and obtaining a polyesterimide composition with improved melt flow index and impact strength based on a polyesterimide (PEI) matrix polymer reinforced with sized carbon fiber (carbon fiber, CF) as a filler.

This task is achieved by the fact that polyetherimide compositions filled with carbon filler are obtained by pre-treatment of carbon fiber with a sizing composition - a mixture of polyesterimide and di(4-aminophenyl)-methane (DAFM). In this case, the following ratios (wt. %) of the components in the filler are taken:

carbon fiber 97.5; PEI 2.46 ÷ 2.08; DAFM 0.04 ÷ 0.42.

The amount of sizing composition to carbon fiber corresponds to 2.5%. The amount of finished carbon fiber in the polyesterimide composition corresponds to 20 wt. %. Treatment with such a sizing composition increases the wettability of the carbon fiber with polyesterimide, and allows repeated, if necessary, heat treatment of the resulting product without changing the properties of the sizing composition.

Finished fibers are obtained by treating carbon fiber with a sizing composition in an ultrasonic bath CD-4820 with an operating frequency of 46 kHz. Polyetherimide compositions of the present invention are obtained by pre-mixing the polymer matrix and sized carbon fiber using a high-speed homogenizer Multi function disintegrator VLM-40B. Then the polymer mixture is extruded using a laboratory twin-screw extruder with three heating zones at processing temperatures of 200 °C, 315 °C, 355 °C. Used carbon fiber brand RK-306 (IFI Technical Production) and polyetherimide (PEI) brand ULTEM-1010, which is a polycondensation product of 1,3-diaminobenzene and dianhydride 2,2'-bis[4(3,4-dicarboxyphenoxy)phenyl]- propane formula:

with a reduced viscosity of 0.61 dl/g, measured for 0.5 wt. % solution in chloroform, di(4-aminophenyl)-methane and chloroform, brand "HCh".

Below are examples illustrating the method of obtaining finished carbon fibers using a sizing composition.

Example 1. Obtaining finished CF with 2.46 wt. % PEI and 0.04 wt. % DAFM.

23.4 g (97.5 wt. %) of HC with a fiber length of 3 mm is placed in a three-necked reaction flask and a solution obtained by dissolving 0.59 g (2.46 wt. %) of PEI and 0.01 g (0. 04 wt.%) DAFM in 125 ml of chloroform (0.32% solution). The flask is placed in a water bath of an ultrasonic bath at a temperature of 20 °C, the ultrasound is turned on and incubated for 3 minutes. After that, a stirrer is placed in the flask, a direct condenser is connected, and the supply of gaseous nitrogen is turned on. The stirrer is turned on, and the contents of the flask are heated and chloroform is distilled off according to the regime: 35 ° C - 1.5 minutes; 45 °С - 1.5 min.; 55 °С - 1.5 min.; 60 °C - 1.5 min.

The dressed fiber is dried in an oven under vacuum at 61-62 °C for 1.5 hours.

Example 2. Obtaining finished HC with 2.38 wt. % PEI and 0.12 wt. % DAFM.

23.4 g (97.5 wt.%) of HC with a fiber length of 3 mm is placed in a three-necked reaction flask and a solution obtained by dissolving 0.57 g (2.38 wt.%) of PEI and 0.03 g (0. 12 wt.%) DAPM in 125 ml of chloroform (0.32% solution). The flask is placed in a water bath of an ultrasonic bath at a temperature of 20 °C, the ultrasound is turned on and incubated for 3 minutes. After that, a stirrer is placed in the flask, a direct condenser is connected, and the supply of gaseous nitrogen is turned on. The stirrer is turned on, and the contents of the flask are heated and chloroform is distilled off according to the regime: 35 ° C - 1.5 minutes; 45 °С - 1.5 min.; 55 °С - 1.5 min.; 60 °C - 1.5 min.

The dressed fiber is dried in an oven under vacuum at 61-62 °C for 1.5 hours.

Example 3. Obtaining finished HC with 2.29 wt. % PEI and 0.21 wt. % DAPM.

23.4 g (97.5 wt.%) of HC with a fiber length of 3 mm is placed in a three-necked reaction flask and a solution obtained by dissolving 0.55 g (2.29 wt.%) of PEI and 0.05 g (0. 21 wt.%) DAPM in 125 ml of chloroform (0.32% solution). The flask is placed in a water bath of an ultrasonic bath at a temperature of 20 °C, the ultrasound is turned on and incubated for 3 minutes. After that, a stirrer is placed in the flask, a direct condenser is connected, and the supply of gaseous nitrogen is turned on. The stirrer is turned on, and the contents of the flask are heated and chloroform is distilled off according to the regime: 35 ° C - 1.5 minutes; 45 °С - 1.5 min.; 55 °С - 1.5 min.; 60 °C - 1.5 min.

The dressed fiber is dried in an oven under vacuum at 61-62 °C for 1.5 hours.

Example 4. Obtaining finished HC with 2.21 wt. % PEI and 0.29 wt. % DAPM.

23.4 g (97.5 wt.%) of HC with a fiber length of 3 mm is placed in a three-necked reaction flask and a solution obtained by dissolving 0.53 g (2.21 wt.%) of PEI and 0.07 g (0. 29 wt.%) DAFM in 125 ml of chloroform (0.32% solution). The flask is placed in a water bath of an ultrasonic bath at a temperature of 20 °C, the ultrasound is turned on and incubated for 3 minutes. After that, a stirrer is placed in the flask, a direct condenser is connected, and the supply of gaseous nitrogen is turned on. The stirrer is turned on, and the contents of the flask are heated and chloroform is distilled off according to the regime: 35 ° C - 1.5 minutes; 45 °С - 1.5 min.; 55 °С - 1.5 min.; 60 °C - 1.5 min.

The dressed fiber is dried in an oven under vacuum at 61-62 °C for 1.5 hours.

Example 5. Obtaining finished HC with 2.12 wt. % PEI and 0.38 wt. % DAFM.

23.4 g (97.5 wt.%) of HC with a fiber length of 3 mm is placed in a three-necked reaction flask and a solution obtained by dissolving 0.51 g (2.12 wt.%) of PEI and 0.09 g (0. 38 wt.%) DAPM in 125 ml of chloroform (0.32% solution). The flask is placed in a water bath of an ultrasonic bath at a temperature of 20 °C, the ultrasound is turned on and incubated for 3 minutes. After that, a stirrer is placed in the flask, a direct condenser is connected, and the supply of gaseous nitrogen is turned on. The stirrer is turned on, and the contents of the flask are heated and chloroform is distilled off according to the regime: 35 ° C - 1.5 minutes; 45 °С - 1.5 min.; 55 °С - 1.5 min.; 60 °C - 1.5 min.

The dressed fiber is dried in an oven under vacuum at 61-62 °C for 1.5 hours.

Example 6. Obtaining finished HC with 2.08 wt. % PEI and 0.42 wt. % DAPM.

23.4 g (97.5 wt.%) of HC with a fiber length of 3 mm is placed in a three-necked reaction flask and a solution obtained by dissolving 0.5 g (2.08 wt.%) of PEI and 0.1 g (0. 42 wt.%) DAFM in 125 ml of chloroform (0.32% solution). The flask is placed in a water bath of an ultrasonic bath at a temperature of 20 °C, the ultrasound is turned on and incubated for 3 minutes. After that, a stirrer is placed in the flask, a direct condenser is connected, and the supply of gaseous nitrogen is turned on. The stirrer is turned on, and the contents of the flask are heated and chloroform is distilled off according to the regime: 35 ° C - 1.5 minutes; 45 °С - 1.5 min.; 55 °С - 1.5 min.; 60 °C - 1.5 min.

The dressed fiber is dried in an oven under vacuum at 61-62 °C for 1.5 hours.

Composite materials containing 20 wt. % finished with a mixture of PEI and DAFM carbon fibers.

Table 1 shows the compositions, melt flow rates and impact strength of compositions containing hydrocarbons according to examples 1-6, treated with various amounts of sizing composition.

Table 1

Composition (wt.%)
PTR,
g/10 min А _r , kJ/m²
11 J No tension With tension PEI 13.2 75.5 6.1 PEI + 20% HC raw 3.4 30.3 5.1 According to example 1 7.23 30.35 6.03 According to example 2 7.55 31.46 6.13 According to example 3 7.64 33.77 7.44 According to example 4 7.83 35.87 8.24 According to example 5 8.41 35.28 8.04 According to example 6 8.52 34.97 7.75

where MFR is the melt flow rate, A _p is the impact strength.

As can be seen from the data, polymer compositions containing sized CFs (nos. 1-6) exhibit higher melt flow and impact strength compared to a composite containing untreated carbon fiber.

The technical result of the invention is to improve the melt flow and impact strength of the created carbon fiber polyesterimide compositions due to the introduction of a sizing composition - polyesterimide and di(4-aminophenyl)-methane, which increases the wettability of the filler and increases the boundary interactions between the filler and the polyesterimide matrix.

Claims (5)

1. A method for producing sizing carbon fibers intended for structural polymeric materials based on sizing carbon fiber by applying a sizing component from a solution followed by drying in an oven under vacuum at 61-62 ° C, characterized in that the sizing consisting of polyesterimide (PEI) and di(4-aminophenyl)methane (DAFM), are applied from a solution with a mass concentration of 0.32 wt.% in a highly volatile organic solvent chloroform and a stepwise increase in temperature is carried out with simultaneous distillation of the solvent and exposure to ultrasound with an operating frequency of 46 kHz along mode: 20°C - 3 min; 35°C - 1.5 min; 45°C - 1.5 min; 55°C - 1.5 min; 60°C - 1.5 min, and the quantitative ratio of the components corresponds, wt.%: carbon fiber 97.5 PEI 2.46–2.08 DAFM 0.04–0.42 2. Finished carbon fiber for structural products in additive technologies, obtained by the method according to p. 1. 3. Polyetherimide composition used in the manufacture of structural products in additive technologies, containing a polymer matrix based on polyesterimide and finished carbon fiber, characterized in that the finished carbon fiber according to claim 2 is used, and the quantitative ratio of components in the composite material corresponds, wt.% : polyetherimide 80 finished carbon fiber 20